This invention relates to improvements in a command speed generator system for an elevator car.
Speed feedback control systems for controlling the speed of the elevator car in accordance with a command deceleration signal are employed in order that the elevator car is decelerated with a comfortable ride maintained and lands accurately at that floor of a building an which the car is predetermined to be stopped due to a call resistered thereon or on the elevator car. It has been recently proposed to cause the elevator car to decelerate and land at such a floor by using an electronic computer.
To this end, it has been a common practice to count an output from a pulse generator connected to a hoist motor involved to determine the amount of movement of the elevator car. When a position sensor disposed in an associated hoistway senses that the elevator car has reached a predetermined distance short of that floor at which the elevator car is predetermined to land, the distance of movement of the car is entered into the electronic computer at the beginning of each of the calculating time periods. The electronic computer calculates a residual distance to the abovementioned floor by subtracting the distance of movement of the car from the predetermined distance. Following this, the computer reads out a command deceleration signal stored with respect to the calculated residual distance in a read only memory device involved therefrom. Then, the speed of the elevator car is controlled in accordance with the command deceleration signal thus read out.
The electronic computer is normally arranged such that the calculating or an interrupting time period is not normally synchronized with the time of operation of the position sensor. Therefore, when the elevator car reached the position sensor, the calculation of the residual distance is not always immediately initiated. A time point at which the position sensor is operated occurs, in many cases, between the adjacent calculating time periods of the electronic computer with the result that the elevator car may travel a distance L in the worst case where L is equal to the product of a car speed v and the calculating time period .DELTA.t. However, the electronic computer has therein the predetermined distance (which is designated by the reference character A) stored at the beginning of the calculating time period, resulting in the setting of a magnitude of distance which is greater by the distance L than the actual distance. In other words, while the command deceleration signal to be delivered must properly have a magnitude V.sub.1 bearing a relationship to the residual distance of (A-L), a command deceleration signal is actually delivered having a magnitude V.sub.2 bearing a relationship to the residual distance A and is therefore greater than the magnitude V.sub.1. That is, there has been delivered a command deceleration signal having an error with respect to the landing of the elevator car. The magnitude V.sub.2 is greater than that of the proper command deceleration signal resulting in a deterioration of the landing accuracy.
Accordingly, it is an object of the present invention to eliminate the objection to the prior art practice as described above by the provision of a new and improved command speed generator system for an elevator car for generating a command deceleration signal free from distance error, regardless of the time point where an output from a position sensor involved is entered into an associated electronic computer.